Apparatuses for measuring blood glucose concentration are well known. See, for example, U.S. Pat. No. 4,750,496. In an article entitled "Novel Blood Glucose Monitoring Method and ISFET Biosensor Applied to Transcutaneous Effusion Fluid" by J. Kimura, N. Ito, T. Kuriyama, published in J. Electrochem. Soc., Vol 136, No. 6, Jun. 1989, pp. 1744-1747, interstitial fluid was withdrawn via a pump and applied to an ISFET biosensor. The sensor was able to detect chemical components of the interstitial fluid.
The drawback of such an apparatus appears to be the cumbersome requirement of the pump, separate and apart from the sensor, and the requirement of drawing out a large amount of interstitial fluid in order to sense the chemical components therein. This prohibits the use of an interstitial fluid which can be "permanently" attached to a person or an animal for the detection of chemical components of the fluid on an "as needed" basis.